# What is a leap year and how is it different from a normal year?

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In everyday life, the leap year is determined, starting in 2000, very simply: to the last leap year the number 4 is added and the resulting year will be a leap year. For example, the leap years will be the years 2016, 2020, 2024, etc.

However, sometimes, once every 100 and once every 400 years, adjustments are made. Therefore, by adding the number 4, it is possible to determine a leap year only until 2100. The general algorithm for determining a leap year, according to the current Gregorian calendar, is as follows:

Formula for calculating a leap year in Excel

Based on the algorithm, we have developed the following formula for determining a leap year:

At the same time, the cell “A1” should have a year, for example, 2019, 2100, 1917, etc.

Similarly, you can calculate the number of days in February of a given year:

Here is an example calculation using our formula:

 2000 Leap 2015 Leapless 2001 Leapless 2016 Leap 2002 Leapless 2017 Leapless 2003 Leapless … … 2004 Leap 2095 Leapless 2005 Leapless 2096 Leap 2006 Leapless 2097 Leapless 2007 Leapless 2098 Leapless 2008 Leap 2099 Leapless 2009 Leapless 2100 Leapless 2010 Leapless 2101 Leapless 2011 Leapless 2102 Leapless 2012 Leap 2103 Leapless 2013 Leapless 2104 Leap 2014 Leapless 2105 Leapless

As you can see, the calculation gives a full correspondence of the years to lent or leapless years.

Pay attention to 2000 and to 2100. The first is divided without a remainder into 4, and 100, and 400, therefore it is a leap year. The second is a multiple of only 4 and 100, so it is NOT leap.

Strictly speaking, the above calculation algorithm is not entirely accurate. Because the average duration of the tropical year (the time between the two spring equinoxes) is approximately 365 days 5 hours 49 minutes.

Those. a year on average exceeds 365 days by about 5 hours 49 minutes or 0.24236 days. Whereas, according to the indicated algorithm, the excess is 0.2425 days. The difference is 0.00014 days. Therefore, if you use the specified algorithm, each next year the error will be 0.00014 days. After 1 / 0.00014 = 7199 years, the error in determining the time between the two spring equinoxes will be 1 day already. However, more than 7 thousand years is a matter of a very distant future and it is not known whether humanity will even exist by then. And will Excel be relevant?

In the meantime, in the next thousand years, as well as for the past tense, you can quite easily use the above formula for determining a leap year in Excel.

## Who brought leap years into the calendar?

Ancient Roman astronomers were well aware that a year on Earth lasts 365 days and a few more hours. Because of this, the calendar year, which then consisted of a constant number of days, did not coincide with the astronomical one. Over hours gradually accumulated, turning into days. Calendar dates gradually shifted and deviated from natural phenomena - for example, the equinoxes. A group of astronomers, led by Sozigen, who worked at the court of Julius Caesar, suggested adjusting the calendar. According to the new calendar, every fourth year was extended by one day. This year began to be called bis sextus, which is translated from Latin means "Second sixth". In Russian, this word was transformed into Leap - that's what we call it to this day.

By order of Julius Caesar, a new calendar was introduced, starting from the 45th year BC. After the death of the emperor, a malfunction occurred in the calculation of leap years, and the countdown began anew from the 8th year of our era. Therefore, in our time, even years are leap years.

It was decided to add a day to the last, shortest month of the year, which already had "not enough days." In ancient Rome, the New Year was celebrated on March 1, so that the extra 366th day was added to February. The new calendar began to be called "Julian" in honor of Caesar. By the way, the Orthodox and some other churches still live on the Julian calendar - this is a tribute to tradition.

## And again, calendar changes

Astronomical observations continued, methods became more and more accurate. Over time, stargazers realized that the duration of the earth's year is not 365 days and 6 hours, but a little less. (It is now known that a year lasts 365 days 5 hours 48 minutes and 46 seconds).

The use of the Julian chronology led to the fact that the calendar began to be late from the real course of time. Astronomers have noticed that the vernal equinox comes much earlier than the day allotted to it according to the calendar, that is, March 21. There was a need to adjust the calendar, which was done by decree of Pope Gregory XIII in 1582.

To compensate for the discrepancy, we decided to establish leap years according to the new rule. It was necessary to reduce their number, which was done. From that moment on, leaps are still considered to be all years that are multiples of four, except those divisible by 100. For an even more accurate reckoning, years that are divisible by 400 are still considered leap years.

That is why 1900 (like 1700 and 1800) was not a leap year, and 2000 (like 1600) was one.

The new calendar was named after the Pope Gregorian - all countries of the world currently live on it. The Julian calendar is used by a number of Christian churches - including the Russian Orthodox Church.

## How is a leap year different from others?

Only one - it has 366 days, with an additional day assigned to February. Despite the fact that the year now starts on January 1, which means that the last month of the year is December, we still give extra days to February. He is the shortest - we will pity him!

And we will rejoice for those who were born on February 29 in a leap year. These "lucky ones" celebrate their birthday every four years, which makes this event more long-awaited and desired than other people.

## What happens in a leap year?

Leap years were chosen for the main sporting event of mankind - the Olympics. Now in leap years, only the Summer Games are held, and winter - with a two-year shift. The sports community adheres to the most ancient tradition established by the first Olympians - the ancient Greeks.

It was they who decided that such a grand event should not happen too often - once every four years. The four-year cycle coincided with the alternation of leap years, so modern Olympics began to be held precisely in leap years.

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